1. Field of the Invention
This invention relates to a novel method of immobilizing enzymatically active materials and, more particularly, to a method of immobilizing an enzymatically active material to a water-insoluble polyanion which comprises bringing a polycation-containing aqueous medium and the enzymatically active material into contact with the water-insoluble polyanion.
2. Description of the Prior Art
Conventionally, a number of techniques for immobilizing enzymatically active materials are well known which include, for example, the method of chemically combining an enzymatically active material with another enzymatically active material or an insoluble carrier by covalent or ionic bonding and the method of entrapping an enzymatically active material within a water-insoluble substance or microcapsules. Among the rest, the adsorption method in which an enzymatically active material is fixed on the surfaces of an inert carrier by ionic or other physical force has several advantages over other immobilization methods. For example, the adsorption method permits an enzymatically active material to be immobilized under very mild conditions and bound loosely to a carrier. Thus, the enzymatically active material suffers little damage from the immobilization procedure and, after being once immobilized, it undergoes only a slight degree of deactivation. Moreover, the adsorption method permits the enzymatically active material to be fixed in the vicinity of the surfaces of the carrier. Accordingly, when a substrate is brought into contact with the immobilized preparation of the enzymatically active material, the substrate readily spreads over the enzymatically active material, so that it can exhibit high activity even in the immobilized state. Furthermore, it is possible to prepare and pretreat the carrier in the absence of enzymatically active material. Thus, as compared with the preparation and pretreatment of a carrier in other immobilization methods, greater latitude is given in determining the type of carrier used and the method of preparation. This makes it possible to select a carrier highly suitable for the intended purpose. A further advantage of the adsorption method is that the immobilization procedure can be carried out in a culture vessel or the like. This serves not only to largely decrease the risk of contamination with undesired microorganisms during the procedure for immobilizing an enzymatically active material, but also to simplify the immobilization procedure to a remarkable degree.
With all these advantages, the adsorption method still has many disadvantages and cannot be regarded as a satisfactory method of immobilizing enzymatically active materials. Specifically, as compared with the above-described chemical and physical immobilization methods, the adsorption method is disadvantageous in that the immobilization procedure has low efficiency and requires a long period of time. Moreover, since the adsorption depends largely on the surface condition of the carrier the enzymatically active material is liable to desorption due to the change in the surface conditions of the carrier during use. Furthermore, the adsorptive power of the enzymatically active material to the carrier is so low that, during the immobilization of the enzymatically active material or during the use of the resulting immobilized preparation, the enzymatically active material tends to be released from the carrier under the influence of mechanical shock and the like. In addition, when living microbial cells and the like are used as the enzymatically active material, most of the newly grown cells are released from the carrier. This makes the adsorption method unsuitable for the immobilization of growing microbial cells.